1. Field of the Invention
The invention relates to organopolysiloxane compositions curable by condensation reaction, to methods for producing them and to their use, more particularly for producing artificial stones.
2. Description of the Related Art
Organopolysiloxane resins which comprise condensable reactive silyl units, hydroxyl groups for example, and hydrolyzable radicals such as alkoxy groups, are crosslinked by polycondensation typically in the presence of catalysts such as zinc, lead, cobalt or titanium compounds, for instance. Reference in this regard may be made for example to A. Tomanek, Silicone & Technik, [published by Wacker Chemie GmbH, Munich]—Munich, Vienna Hanser, 1990 (ISBN 3-446-16032-9), pages 72 and 73.
Likewise suitable are organosilanes or organopolysiloxanes whose units include a guanidyl unit and which are described in the literature as effective, alternative metal-free curing accelerators. Examples thereof are found in U.S. Pat. Nos. 4,248,993 and 8,372,935.
Moreover, WO-A 2013/101751 and the specifications identified in that publication as prior art describe zinc(II) and zirconium(IV) compounds or salts and also further metals as condensation catalysts for polyorganosiloxane systems.
These curing accelerator or catalyst systems have the disadvantage that, when used in an amount sufficient to achieve sufficiently rapid curing at elevated temperatures, they are active even at room temperature and, in the presence of silanol units and optionally alkoxysilyl units, they directly accelerate the polycondensation reaction and hence the curing of the polyorganosiloxane compositions, meaning that the working time, expressed by the potlife, of the mixtures is very short, and so it is difficult to carry out further processing of the prematurely crosslinked polyorganosiloxane compositions, for example, in a subsequent shaping operation.